Interesting interview on radio 4 this morning about this. Commentator from a security company specialising in Identity theft banged on about the 'balloon effect' where criminals target other areas in response to increased security.
But this interview was phrased in terms of identity theft. Which is odd, considering that these are blank documents with no identity information on them. They're not yet associated with people. What they do have is the possibility of exploiting the institutional relationship between identity and structured institutions of the state. If you're committing identity 'theft' (a problematic term), then you don't need blank identity documents.
Of course, I wouldn't be surprised if this theft is used to add to the vulnerability of the current mechanisms of identity in arguments for apparently more secure identity cards. Which could never be stolen en mass or otherwise subverted, could they?
edit: register article on this here and Guardian article here